1. Field of the Invention
The invention relates to the acoustic wave methods and systems for presence or movement detection and for distance or direction finding in the case of having a plurality of ultrasound type transmitter and receiver transducers. In particular this invention refers to condition responsive early indicating systems that exploit the registration of an occasional disturbance of ultrasonic wave beams in the manner of their reflection, refraction by edge diffraction and interference by shadowing, which disturbance has been made by either an intruding subject or a trespasser.
2. Description of Related Art
At present there exist methods and systems of ultrasound intrusion detection in an entire volumetric surveillance areas, in which areas there are being used different arrangements of transmitting and receiving transducers, at least namely:                fan-shaped or matrix arrangements of transmitter and receiver transducers for stationary vector directing surveillance, e.g. U.S. Pat. No. 5,920,521 and U.S. Pat. No. 4,582,065 respectively;        solitary arrangement of transmitter and receiver couples for scanning all over the surveyed area with narrow clusters of ultrasound beams, e.g. US 2004/0140886 A1; U.S. Pat. No. 4,644,509; U.S. Pat. No. 5,309,144;        multi-seat arrangement of receivers along the perimeter of protected area for detecting an occurrence of ingress or egress intrusion thru the vicinity of protected area perimeter, e.g. U.S. Pat. No. 5,483,224 and U.S. Pat. No. 5,872,516;        single-row or multi-row arrangement of transmitting and receiving transducers for realizing various processing operations with the help of reflected ultrasound beams, in particular:                    detection any strange subject inside the surveyed area, e.g. U.S. Pat. No. 5,761,155, U.S. Pat. No. 6,411,202 B1 and U.S. Pat. No. 6,518,915B2;            measurement of distance to intruded subjects or to the level of interface of liquid and granular materials, e.g. U.S. Pat. No. 4,949,074, U.S. Pat. No. 5,231,608 and U.S. Pat. No. 5,131,271, U.S. Pat. No. 6,323,441B1 respectively;                        isolated arrangement of transmitter inside an enclosed area and positioning the receiver outside this enclosed area with the aim of detecting an occurrence of destroying the isolation of said protected area by an intruder, e.g. U.S. Pat. No. 4,807,255, U.S. Pat. No. 5,638,048, U.S. Pat. No. 6,430,988.        
As is evident from the delivered above the elucidative examples, the modern methods and systems for ultrasound intrusion detection utilize preferably the phenomenon of reflection of ultrasound beams from strange subjects that occurred inside a surveyed area. Meanwhile, it is the known fact that the process of emitting-reception of airborne ultrasound signals depends strongly upon air ambient conditions (temperature, moisture, atmospheric pressure, etc.) and therefore it is restricted spatially. In turn, this restriction predicts the limitations upon volumetric dimensions of surveyed area and consequently on the capability of earlier warning detection of either an intruding subject or a trespasser. The alternative enhancement of the entire protected space might be realized by attaching to the ultrasound-surveyed area the proper number of adjacent areas, which areas were being surveyed with use of different physical principles of intrusion detection (infrared, microwave, light level sensing, etc.), e.g. see U.S. Pat. No. 4,857,912 and U.S. Pat. No. 6,127,926. Unfortunately, such a would-be method and arrangement will lead to hardware and software complexity, low reliability and great cost of an intrusion protection system as a whole. Nevertheless, it is necessary to establish such very method of intrusion protection that features with high reliability and self-defense, and meets the requirements to the multi-echelon arrangement of the protection systems of critical objects. Those strong requirements are delivered at least in the following regulations for such evidently critical objects as Nuclear Power Plants:                Defense-in-Depth in Nuclear Safety, IAEA INSAG-10, LAEA, Vienna, 1996.        Method for Performing Diversity and Defense-in-Depth Analysis of Reactor Protection Systems. NUREG for U.S.NRC/Prepared by G.G. Preckshot-Lawrence Livermore National Laboratory/Manuscript date: December 1994.        
Furthermore, it seems to be relevant to emphasize some unique features of ultrasound that make it attractive for the purpose of faultless intrusion protection, namely:                ultrasound waves are being emitted in the form of narrow directional beams and consequently do not travel around corners well, so beam patterns of the directional beams may be easily reflected or shielded by an intruded subject; or they may be refracted, i.e. diffracted by the edge of a subject having penetrated them into small part of their peripheral lobes;        narrow solid angle of directional reception of airborne ultrasound may be obtained with relatively small dimensions of hidden receivers;        ultrasound is not influenced by regular “white noise” of an environment, especially by an industrial ambient, being either inside or outside.        
Besides, at the present time the ultrasound processing methods and instruments are being well practiced in even multi-modular hierarchical imaging, detecting and measuring systems that contain the similar ultrasonic instrumentation and hence are reliable, convenient and low-cost. This real advancement of the processing architecture is the actual prerequisite for improving ultrasound intrusion protection technology, which the present invention is devoted to.